Because of the revolution of the Earth around the sun, the various faces of a geostationary satellite do not receive the same quantity of solar radiation over the seasons. As a result, there are cyclical variations in temperature on the face +Y and on the face −Y. Thus, during the winter and summer equinoxes (EQ), the faces −Y and +Y have lower temperatures than during the winter (WS) and summer (SS) solstices, as illustrated in FIG. 1. Moreover, the temperature of the faces of the satellite also fluctuates over time. This temperature is approximately equal to 20° C. at the beginning of the life of the satellite and is 70° C. at the end of the life of the satellite. These variations in temperature over the seasons and over time are reproduced on the ground in a vacuum atmosphere during satellite validation tests.
These validation tests are long and complex to carry out.
To facilitate the validation tests on the ground, reducing the variations in temperature over the seasons and over time was envisaged.
For this purpose, the faces +Y and −Y of the satellite were heated by electric heaters during the equinox. Nevertheless, the heaters have limited effectiveness and require the electric power system of the satellite to be oversized. This oversizing notably increases the cost of the satellite.
Moreover, to regulate the temperatures of the faces of Earth-observation satellites, louvers were attached opposite radiators mounted on the outer faces of the satellites. These louvers obscure the outer face of the radiator more or less according to the cooling needs of the satellites. The louvers are mounted pivotably about an axis positioned along a longitudinal edge of the louvers. In the closed position, such louvers obscure all of the outer face of the radiator. The only function of these louvers is to prevent solar radiation from reaching the radiator. Moreover, these louvers require a complex mechanism allowing the rotation of the louvers. This mechanism must have good strength in a variable thermal environment.
Document JP H03 109999 discloses a satellite comprising a device that allows a portion of the incident solar radiation (Ie) to be absorbed mainly during the vernal and autumnal equinoxes and transferred via radiation to the adjacent radiator. This device comprises two heat-radiating plates, each mounted on a supporting arm of a solar panel. Over the course of a day, the two supporting arms and the two heat-radiating plates are rotated about the longitudinal axis of the supporting arms.
Each plate is solid. It has a high-absorptivity, high-emissivity face and an opposite, low-absorptivity face. This latter face is suitable for reflecting solar radiation. The plates are rotated about an axis perpendicular to the longitudinal axis of the supporting arm that supports it. The amplitude of rotation is approximately 180°. The rotation is carried out during certain seasons. Thus, at the vernal and autumnal equinox, the high-absorptivity faces of the two heat-radiating plates are pivoted in such a way as to form an angle of 23° with the radiators.
Thus, the high-absorptivity faces absorb solar radiation and emit heat to the radiators. During the summer solstice, the heat-radiating plate of the supporting arm located on the North side is rotated in order for its low-absorptivity face to be directed towards the solar radiation and be perpendicular to the North radiator. This face is thus exposed towards the sun in order to not heat the South radiator of the satellite when it is exposed to direct solar radiation.
Finally, during the winter solstice, the heat-radiating plate of the supporting arm located on the South side is rotated in order for its low-absorptivity face to be directed towards the solar radiation and be perpendicular to the South radiator.
This device, however, requires one or two additional electric motors. This or these motors make the satellite heavier and increase its manufacturing cost.
Moreover, the satellite of document JP H03 109999 is not secure. If a part or one of the motors for rotating the heat-radiating plates breaks down during a mission, it is difficult to repair them. If, in addition, this breakdown takes place during the solstices, the heat-radiating plates remain in a position that will increase the temperature differences during the other seasons and will endanger the operation of the on-board electronic equipment.